Project Summary/Abstract The metabolic syndrome (MetS), a constellation of conditions and disorders including obesity, insulin resistance/abnormal glucose regulation, nonalcoholic fatty liver disease (NAFLD), elevated circulating LDL- C/HDL-C ratios and triglycerides, and hypertension, is rapidly increasing world-wide and is associated with more severe diseases such as type 2 diabetes and cardiovascular disease. However, the genetic and molecular contributions to the etiology of MetS remain unclear. We recently discovered microRNAs (miR- 33b/a) as key regulators of cholesterol/lipid homeostasis. We have now employed genome-wide association studies (GWAS) to uncover the miR-128-1 microRNA as linked to cholesterol/lipid abnormalities, obesity, type 2 diabetes and recent human positive selection. Our preliminary in vitro and in vivo studies in mice have confirmed that miR-128-1 exerts profound effects on metabolic homeostasis. We propose here to test the hypothesis that miR-128-1 represents a central regulator of mammalian energy metabolism, and that human evolutionary adaptation to feast/famine cycles in ancient times led to increased miR-128-1 activity promoting energy storage in certain human populations. While beneficial in times of famine, elevated miR-128-1 activity/levels in present times with profound food abundance in the developed world could contribute to metabolic diseases such as obesity and type 2 diabetes. Both in vitro cell culture and in vivo studies in mouse metabolic disease models (e.g., DIO, ob/ob mice) with antisense targeting of miR-128-1, as well as miR-128-1 KO mice will provide critical mechanistic insights into the role of miR-128-1 in targeting pathways guiding metabolic homeostasis, and whether this microRNA may be suitable for therapeutic targeting to improve prevalent metabolic disorders such as obesity and type 2 diabetes.